Removal of sulfur contaminants from hydrocarbon streams



REMOVAL OF SULFUR CONTAMINANTS FROM HY DROCARBON STREAMS Theodore J. Peters, Somerville, and Albert Gathmau,

Neptune, N.J., assignors to Esso Research and Eng:- neering Company, a corporation of Delaware No Drawing. Filed Jan. 30, 1958, Ser. No. 712,090

6 Claims (Cl. 260-677) This invention relates to the preparation of a substantially isoalkene free C to C normal alkene containing hydrocarbon stream having a reduced sulfur content. In a preferred embodiment, this invention relates to an improved process for the recovery of a substantially isobutylene free normal butylene bearing stream containing a reduced sulfur content from a crude hydrocarbon mixture comprising initially butanes, butylenes, mercaptans and other sulfur contaminants and usually small amounts of C and C hydrocarbons. This invention further relates to the separation of a n-butylene containing stream of low sulfur content from a hydrocarbon stream containing normal and isobutylenes having a higher sulfur content. The term sulfur content or contaminant as employed herein is meant to include sulfur in its elemental form and/or in the form of its various organic and inorganic compounds. This invention further relates to the use of these isoalkene free normal alkene streams containing low sulfur content in the preparation of a1- cohols having the same number of carbon atoms as the alkene, such as secondary butyl alcohol from n-butylene.

There are two processes for the preparation of alcohols from olefins which are in successful commercial operation today. Broadly speaking, the first process comprises the acid extraction technique wherein the hydrocarbon stream containing olefin is contacted with an aqueous mineral acid such as sulfuric or phosphoric to form an acid extract. This acid extract may then be hydrolyzed with steam and/0r water to form the desired alcohol product which may subsequently be finished to a high degree of purity. The second major process suitable for commercial use comprises what is known as the direct hydration technique. In the direct hydration technique the olefins such as butylenes are contacted under severe reaction conditions with Water in the presence of a synthetic acid resin catalyst such as an ion exchange resin possessing essentially a hydrocarbon skeleton combined with a strong mineral acid group, e.g. sulfonic radical.

The removal of sulfur from the olefin feed and/or alcohol product to a point where the alcohol product is acceptable to the trade is a serious problem confronting the manufacturers of these alcohols. The olefin containing hydrocarbon streams employed in the preparation of alcohols is unavoidably contaminated with sulfur contaminants which may be present in various forms. It is accordingly necessary to remove sulfur from the olefin bearing stream as completely as possible without making the process economically unattractive. In general, the prior art has scrub-bed the olefin bearing stream with sulfur removing agents such as aqueous caustic soda or other alkaline agents. While this treatment effects a substantial reduction in sulfur contaminants, there nevertheless appear to be sulfur contaminants which either cannot be or are difiicult to remove by commercial distillation and/or scrubbing techniques. Accordingly, the

alcohol derived from these olefins are contaminated with nited States Pater considerable sulfur, e.g. 20-5O parts per million and require extensive finishing steps to produce a commercially acceptable product. To illustrate the above noted alcohol preparation techniques, a brief description of both types will follow. For the sake of convenience both the direct hydration and acid extraction techniques will be described with reference to the production of secondary butyl alcohol although it is to be understood that this process is amenable to the preparation of the C to C alkenes and the corresponding alcohols.

The acid extraction technique employs cracked gases from petroleum oil refinery streams as a source of the normal butylene to form the acid extract which is subsequently hydrolyzed and distilled to recover the alcohol. These cracked gases may be produced by thermal, catalytic or steam cracking of hydrocarbon oils and are generally a heterogeneous mixture of saturated hydrocarbons, e.g. butanes; normal olefins, e.g. butylenes; tertiary olefins, e.g. isobutylene and smaller quantities of diolefins. Thus a typical mixed C olefin stream will comprise butane 49.4%, n-butylenes 34.2%, isobutylene 14.3%, sulfur contaminants 200 ppm. and small amounts of mixed C and C hydrocarbons 2.1%. It is to be understood, of course, that the composition of the C feed may vary considerably depending on the particular source and it is only necessary for the purposes of this invention that the feed contain substantial amounts of normal butylenes and isobutylenes. The entire process for the preparation of secondary butyl alcohol via this general acid hydrolysis route comprises feeding a mixed C olefin stream such as described above first through an aqueous caustic scrubber to remove a substantial amount of the objectionable sulfur contaminants. While sub stantially all of the H 8 is removed by the caustic wash, minor amounts of mercaptan remain and are present in a suflicient amount to degrade the alternate alcohol product. Preferably, the olefin feed is in a mixed liquid and gaseous phase. The caustic scrubbed hydrocarbon feed is then passed through an isobutylene extraction unit wherein the feed is treated with an aqueous sulfuric acid solution of medium strength. With specific sulfuric acid concentrations the isobutylene is selectively extracted from the olefin mixture. The aqueous acid extract of isobutylene is removed as a separate phase and may be hydrolyzed to recover isobutylene for its well-known uses which are not pertinent to this invention. The remaining portion of the feed comprising principally butanes and normal butylenes is then passed through a normal butylene extraction zone wherein the hydrocarbon stream is contracted with a stronger sulfuric acid solution which selectively extracts the n-butylenes. The aqueous acid extract containing n-butylene is then passed to a hydrolysis zone wherein steam and water are employed to hydrolyze the extract forming crude secondary butyl alcohol. The crude alcohol may then be treated by various known finishing techniques to recover a relatively pure alcohol if desired.

In the direct hydration technique the C olefin feed is treated with caustic and isobutylene is extracted as above described. The remaining normal butylene containing feed is passed with water generally in liquid phase, although a liquid-gaseous phase may be employed, through a closed conversion zone under elevated temperatures and usually elevated pressures in contact with a sulfonated synthetic ion exchange resin in its acid form. One such typical resin is known as Dowex 50X8 made by the Dow Chemical Co. which comprises a sulfonated resinous copolymer of about 92% styrene and 8% divinyl benzene and contains about 44 to 50% moisture and about 12 to 16% sulfur in the sulfonate form, based on anhydrous resin. It is to be understood that the specific resin composition employed in the direct hydration technique is one of choice and may be selected from numerous resins now on the market. The crux of this invention relates to the production of a substantially isobutylene free normal but'ene containing stream having a reduced sulfur content which is accomplished by utilizing a glycol wash subsequent to the isobutylene extraction stage. Although ethylene glycol is the preferred scrubbing agent, any water soluble glycol may be employed. These include diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol and the like. The scrubbing operation'may be carried out by bubbling the C gas through a tower filled or partially filled with. the glycol. In such towers to. insure adequate intimate contact between the gas and liquid, it. is conventional to employ baffles, plates or packing. A preferred technique especially amenable for commercial processes is to pass the contaminated C4 gaseous stream countercurrently through a downwardly flowing-stream of glycol. The glycol may be regenerated by distilling off sulfur contaminants with or without the use of azeotrope formers such as water. Since this butene stream may be employed for the production of alcohols either via the direct hydration route or the acid extraction process, a full description for the production of alcohols via one of the processes will be given for the purpose of amplifying the disclosure.

A crude refinery C olefin stream containing butane 40 to 60%, isobutylene 7 to 20%, small amounts of C and C hydrocarbons, and n-butylenes 20 to 42% is contacted with aqueous caustic soda of from 12 to 17 B. or other known sulfur removing alkaline agents in a scrubbing zone which may be of conventional design. Although not required, elevated temperatures and pressures may be employed in this stage. The caustic treated olefin feed is then contacted with sulfuric acid of preferably of 60 to 70 wt. percent in a volume ratio generally from 5 to 20 volumes of liquid hydrocarbon per volume of sulfuric acid. Conditions within the extraction zone are preferably maintained between 50 to 120 F. with pressures of from-125 p.s.i.g. These conditions are not only necessary for the efiicient and selective extraction of isobutylenes, but have been found to be necessary for the conversion of remaining sulfur contaminants into compounds which can be removed by glycol scrubbing although caustic or other alkaline agents are not effective. The remaining hydrocarbon stream substantially free of isobutylene is then passed through a scrubbing zone in contact with ethylene glycol whereby said contaminants are absorbed in the glycol. At this point the isobutylene free (i.e. about 1%) feed may be employed in the well-known direct hydra-- tion technique as generally noted above or in the acid extract hydrolysis which will be defined in'more detail below. The distillate now substantially reduced in sulfur content and being substantially free from sulfur contamination is then passed through a conventional normal butylene extraction zone wherein the hydrocarbon stream is contacted with sulfuric acid having a concentration of from 70-80 wt. percent, whereby n-butylenes. are selectively extracted. In the n-butylene extraction zone a substantially greater ratio of acid to hydrocarbon feed. is employed to effect a greater recovery of n-butylenes present.- For example, a ratio of from 1-10 liquid volumes of hydrocarbon per volume of sulfuric acid is employed. Reaction conditions for the nbutylene extractionmay comprise a temperature of 80 to 135 F. and preferably 105-115 F. and a pressure 015.515, to 125 p.s.i.g., preferably 85-95 p.s.i.g. The aqueous normal butylene acid extract is then passed to'a final hydrolysis stage wherein the extract is contacted' with water and/or steam under atmospheric or elevated pressures, e.g. up. to 100 p.s.i.g., and elevated temperatures of from 200-300 F. In the hydrolysis stage polymers, olefins and ethers formed as a result of the dilution of the concentrated sulfuric acid are removed overhead and crude secondary butyl alcohol which is substantially sulfur-free is recovered as a side stream.

it has been discovered that sulfur contaminants which cannot be removed by normal sulfur removal techniques such as alkali scrubbing and pre-distillation procedures are converted into higher boiling sulfur compounds during the instant isobutylene extraction stage and that these higher boiling sulfur compounds can be absorbed from the n-butylene stream to produce a normal butylene containing stream substantially free of sulfur compounds. The sulfur content, however, is concentrated as the process progresses since substantially no sulfur is removed with the isobutylene acid extract anda disproportionately small amount of sulfur is carried off with the butanes. The increase in sulfur content on a weight percent basis with regard to the final n-butylene extract will depend on the proportionate amounts ofthe butanes, isobutylenes and n-butylenes present'in the crude feed.

Distillation o-f the feed prior to isobutylene extraction does not effect an appreciable removal of sulfur since prior to the extractionthe remaining sulfur contaminants boil in the range of the C stream.

Example A mixed C olefin-feed having-the approximate composition described previously was first scrubbed with aqueous caustic of 15 B. at ambient conditions. The caustic scrubbed feed was then extracted with 65-66% sulfuric acid at a temperature of about F. and a ressure of p.s.i.g.- with 9 volumes of hydrocarbon per volume of sulfuric acid. The substantially isobutylene free 0., hydrocarbon stream was bubbled through a train of two sintered glass scrubbers containing ethylene glycol to remove sulfur contaminants therefrom which could not be removed by distillation or caustic scrubbing. The normal'butylene comprising stream was then extracted from the hydrocarbon phase at F., a pressure of 90 p.s.i.g. with 76-77 wt. percent sulfuric acid using a hydrocarbon to acid ratio of about 2 /2 to 1. The acid extract was then hydrolyzed with steam and water at about 20 p.s.i.g. and 250 F. to produce secondary butyl alcohol. A crude alcohol of about 72% purity was recovered by distillation. To demonstrate the effectiveness, analyses were'made of the sulfuric content of the isobutylene free C stream before and after scrubbing with ethylene glycol and of the used ethylene glycol from the scrubbers'with the following results.

The above data show the effectiveness of ethylene glycol to remove the nonacidic sulfur compounds from the gas fed to the n-butylene' extraction section of the secondary butyl alcohol unit.

What is claimed is:

1. A processfor'the preparation of a substantially isoalkene-free C to C normal alkene-containing:hydrocarbon stream having a reduced sulfur content which C0iilprises scrubbing a C to C hydrocarbon stream containing normal alk'enes, isoalkenes and contaminated with sulfur compounds with an alkaline agent to substantially reduce sulfur contaminants contained therein, extracting'isoalkenefrom said scrubbed hydrocarbon stream with 60-70 wt; percent sulfuric acid at 50 to F. and a pressure'of 15 to psig; whereby remaining sulfur contaminants are converted to higher boiling compounds, scrubbing the resultant substantially isoallienefree hydrocarbon stream with a watersoluble glycol to Lb... .LJ"

further reduce remaining sulfur contaminants in said isoalkene-free hydrocarbon stream and recovering a substantially sulfur-free normal alkene-containing stream suitable for the production of high purity alcohol.

2. A process in accordance with claim 1 wherein said water soluble glycol is ethylene glycol.

3. A process in accordance with claim 1 wherein said glycol is propylene glycol.

4. A process in accordance with claim 1 wherein said glycol is diethylene glycol.

5. A process for the preparation of a substantially isobutylene-free C to C normal butylene-containing hydrocarbon stream having a reduced sulfur content which comprises scrubbing a C to C hydrocarbon stream containing normal butylenes and isobutylenes and contaminated with sulfur compounds with an alkaline agent to substantially reduce sulfur contaminants contained therein, extracting isobutylene from said scrubbed hydrocarbon stream with 60-70 wt. percent sulfuric acid at 50 to 120 F. and a pressure of 15 to 125 p.s.i.g. whereby remaining sulfur contaminants are converted to higher boiling compounds, scrubbing the resultant substantially isobutylene-free hydrocarbon stream with a water soluble glycol to further reduce the remaining sulfur contaminants in said isobutylene-free hydrocarbon stream and recovering a substantially sulfur-free normal butylene-containing stream suitable for the production of high purity alcohol.

6. A process in accordance with claim 5 wherein said glycol is ethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 1,879,599 Brooks Sept. 27, 1932 2,013,663 Malisofi Sept. 10, 1935 2,139,375 Millar et al. Dec. 6, 1938 2,176,196 Beamer et a1. Oct. 17, 1939 2,394,678 Frankel Feb. 12, 1946 2,514,291 Patterson July 4, 1950 2,560,362 Morrell et a1 July 10, 1951 2,581,065 Arnold -2 Jan. 1, 1952 2,771,497 Hunt et a1 Nov. 20, 1956 2,778,859 Johnson et al. Jan. 22, 1957 2,826,615 Campbell Mar. 11, 1958 

1. A PROCESS FOR THE PREPRATION OF A SUBSTANTIALLY ISOALKENE-FREE C4 TO C6 NORMAL ALKENE-CONTAINING HYDROCARBON STREAM HAVING A REDUCED SULFUR CONTENT WHICH COMPRISES SCRUBBING A C4 TO C6 HYDROCARBON STREAM CONTAINING NORMAL ALKENES, ISOALKENES AND CONTAMINATED WITH SULFUR COMPOUNDS WITH AN ALKALINE AGENT TO SUBSTANTIALLY REDUCE SULFUR CONTAMINANTS CONTAINED THEREIN, EXTRACTING ISOALKENE FROM SAID SCRUBBED HYDROCARBON STREAM WITH 60-70 WT. PERCENT SULFURIC ACID AT 50 TO 120*F. AND A PRESSURE OF 15 TO 125 P.S.I.G. WHEREBY REMAINING SULFUR CONTAMINANTS ARE CONVERTED TO HIGHER BOILING COMPOUNDS, SCRUBBING THE RESULTANT SUBSTANTIALLY ISOALKENEFREE HYDROCARBON STREAM WITH A WATER SOLUBLE GLYCOL TO FURTHER REDUCE REMAINING SULFUR CONTAMINANTS IN SAID ISOALKENE-FREE HYDROCARBON STREAM AND RECOVERING A SUBSTANTIALLY SULFUR-FREE NORMAL ALKENE-CONTAINING STREAM SUITABLE FOR THE PRODUCTION OF HIGH PURITY ALCOHOL. 